1. Field of the Invention
This invention relates to improvements in a swash plate type variable displacement compressor for refrigerant, disposed in a refrigeration cycle, for example, of an air conditioning system of an automotive vehicle.
2. Description of the Prior Art
Swash plate type variable displacement compressors have been well known and put into practical use, for example, in order to pressurize refrigerant in an air conditioning system of an automotive vehicle. A typical example of such a swash plate type variable displacement compressor is disclosed in Japanese Patent Provisional Publication No. 7-103138, in which a journal is movably mounted on a drive shaft so as to be rotatable with the drive shaft. A swash plate is fixedly mounted on the journal in such a manner as to convert a rotational movement of the drive shaft into a linear motion of pistons. The journal and the swash plate are formed or molded independent from each other from the viewpoint of facilitating machining process. Accordingly, the boss section of the journal is formed at its outer peripheral part with an external thread portion, while the central section of the swash plate is formed with a threaded bore (having an internal thread portion). The swash plate is threadedly disposed on the boss section of the journal in a manner that the external thread portion is in engagement with the internal thread portion. As a result, the swash plate is integrally mounted on the journal.
The central section of the swash plate is formed projecting axially and annularly in the opposite directions so as to make the central section thick for the following reasons: The central section formed with the threaded bore requires an axially extending section for providing the internal thread portion. The swash plate is required to be formed at its the central section on its one side surface with engaging sections for a tightening tool for the swash plate. Additionally, The swash plate is required to be formed on the other side surface thereof with seat projections which are to be brought into contact with the surface of a flange of the journal. The seat projections function to restrict a tightening action of the tightening tool. In this regard, the outer peripheral part of one end portion of the thick central section is formed polygonal (for example, hexagonal) so that the tightening tool is engagable with the end portion, while the other end portion of the thick central section is left projecting annularly to serve the seat projection.
As a result, the thickness or axial dimension of the central section of the swash plate is increased over that necessary for forming the internal thread portion. This increases the weight of the swash plate, which is contrary to the requirement of lightening the compressor in weight while being disadvantageous from the viewpoint of production cost.